Overlay for repairing spline and seal teeth of a mated component

ABSTRACT

An overlay for repairing spline and seal teeth of a mated component is disclosed. The overlay is a tube constructed of a weld repair material, the tube having an outer surface and an inner surface. The inner surface is dimensioned to define an aperture sized to receive a plurality of radially spaced splines of the component, the splines of the component arranged to matingly engage a complementary component.

RELATED APPLICATIONS

This application is related to U.S. application Ser. No. 11/104,170entitled “Method of Repairing Spline and Seal Teeth of a MatedComponent” and to U.S. application Ser. No. 11/104,171 entitled“Repaired Spline and Seal Teeth on Mated Components” both of which areassigned to the Assignee of the present invention and which were alsofiled Apr. 12, 2005, the contents of which are hereby incorporated byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to repair of mated components.More particularly, this invention is directed to the repair of splineand seal teeth for an aircraft engine shaft.

BACKGROUND OF THE INVENTION

A gas turbine engine includes a compressor that provides pressurized airto a combustor wherein the air is mixed with fuel and burned forgenerating hot combustion gasses. These gasses flow downstream to one ormore turbines that extract energy therefrom to power the compressor andprovide thrust for powering an aircraft in flight. Typically, a hollowshaft is axially located within the gas turbine to connect thecompressor and turbine for rotation therewith. The shaft may beinterconnected to rotary components of the engine by a series ofradially spaced spline teeth or “splines.” The shaft is typicallymanufactured with a forging, machining and hardening process.

A gas turbine engine rotates in a single direction during operation andis a delicately balanced machine. As the engine is operated normally,the splines on the shaft transmit loads and experience wear, generallyon a single face. Typically, a spline is a thin member that interfaceswith a mating spline on an adjacent part. The face of each spline thattransmits the torque from the turbine to the compressor typically wearsin a predictable pattern. This wear on the load transmitting, orpressure, face of the splines can cause loss of material stock, thecreation of a stress riser on the pressure face and reduction of servicelife of the part, eventually necessitating an engine rebuild. Excessivespline wear could result in failure of both the splines and the engine.

During an engine rebuild, the shaft is inspected to determine the amountof wear on various contacting surfaces, including the spline and sealteeth. The shaft dimensions are compared to a predetermined set ofdimensions and tolerances. A shaft that is not within acceptabletolerances of the predetermined dimensions is typically scrapped and anew shaft is inserted into the rebuilt engine. One reason for scrappingthe shaft is the lack of adequate repair methods for the worn splineteeth. Typically, the wear experienced by the splines is only a fewthousandths of an inch on the pressure face of the splines, withnegligible wear on the opposite faces and tops of the splines.

Efforts to repair the worn face of shaft splines by welding a fillermaterial to the worn face and remachine this face have resulted in arepaired shaft whose dimensions are restored, but have inadequatematerial properties on the pressure face of the spline. One of theseinadequate properties is an undesirable change in grain size within theheat affected zone (HAZ) of the weld area. The HAZ is the region(s)surrounding a weld that are measurably affected by the welding process.If sufficient heat is transferred into a welded substrate,microstructure grain size can increase. A larger grain size isassociated with lower fatigue life and results in a materialmicrostructure that is more susceptible to cracking and will withstandless cyclic stress. Fatigue cracking on the pressure face of splines area known cause of premature failure.

Accordingly, there is a need for a method of repairing the spline teethof a power transmission shaft of a gas turbine engine that overcomes theinadequacies of the prior art.

SUMMARY OF THE INVENTION

The present invention is directed to an overlay for use in repairingspline teeth of a mated component. The present invention provides amethod of minimizing the alteration of physical properties adjacent aweld repair area, by creating a low heat input through welding a minimalamount of repair material to a surface that opposes the worn area, whileproviding a full metallurgical bond between the repair material and thesubstrate.

According to one embodiment of the invention, an overlay for use inrepairing one or more radially spaced splines of a mated component isdisclosed. The overlay comprises a tube comprising a weld repairmaterial, the tube having an outer surface and an inner surface, whereinthe inner surface is dimensioned to define an aperture sized to receivea plurality of radially spaced splines of a component, the splines ofthe component arranged to matingly engage a complementary component.

According to another embodiment of the invention, an overlay for use inrepairing one or more radially spaced splines of an aircraft turbineengine shaft is disclosed. The overlay comprises a tube comprising atleast one material selected from the group consisting of nickel, ironand chromium, the tube having an outer surface and an inner surface,wherein the inner surface defines an aperture dimensioned to receive andcontact radially spaced splines of an aircraft turbine engine shaft.

Other features and advantages of the present invention will be apparentfrom the following more detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings whichillustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a power turbine shaft of an aircraftengine.

FIG. 2 is an enlarged partial sectional view, taken along the line 2-2of FIG. 1, with spline wear exaggerated for clarity.

FIG. 3 is a sectional view of a power turbine shaft illustrating aseries of the splines of FIG. 2 in which the thickness of welded repairmaterial is exaggerated for clarity.

FIG. 4 is an enlarged partial sectional view similar to FIG. 2,illustrating an exemplary contour of a spline to which repair materialhas been attached in accordance with the present invention.

FIG. 5 is an enlarged partial sectional view similar to FIG. 2,illustrating an exemplary contour after remachining of a spline inaccordance with an embodiment of the present invention.

FIG. 6 is a perspective view of the spline portion of the shaft of FIG.1 having an overlay applied over the splines according to an embodimentof the invention.

FIG. 7 is a perspective view of the spline portion of the shaft of FIG.1 having an overlay applied over the splines according to anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

While exemplary embodiments of the invention will be discussed primarilywith respect to a power turbine shaft of a gas turbine engine, it willbe appreciated that the invention can be used with respect to any matedcomponent having splines or seal teeth that matingly engage acorresponding, complementary mated component.

FIG. 1 illustrates a power turbine shaft 10 of an aircraft engine (notshown) to include a splined portion 12 and a seal portion 14. Splinedportion 12 includes a plurality of splines 20 aligned substantiallyparallel to the axis of shaft 10 and radially spaced about shaft 10.

With reference to FIG. 2, a spline 20 is illustrated. Spline 20 has anexterior surface 30 that defines a typical repair area, or worn portion,32 and a non-worn portion 34. Worn portion 32 is defined by a phantomline 38 and a worn surface 36. Before use within an aircraft engine,spline 20 was manufactured to dimensions defined by phantom line 38 andexterior surface 30. During use, worn portion 32 has been lost by spline20, so that exterior surface 30 includes worn surface 36. As theexterior surface 30 at phantom line 38 matingly engaged a tooth, orspline, of a complementary device (not shown), torque was transferredbetween the shaft 10 and the complementary device, resulting in wear andthe loss of worn portion 32. As used in this discussion, worn portion 32is located on the pressure, or contact, face 40 of spline 20. Theopposite face of spline 20 is referred to as non-pressure, ornon-contact, face 42.

FIG. 3 is a portion of the shaft 10 which illustrates a series ofsplines 20 with repair material 50 attached thereto. Preferably, repairmaterial 50 is welded to the spline 20 using a focused energy, or lowheat, input welding process. Even more preferably, the weld puddlecreated is approximately 39.4 mils (˜1 mm) in diameter. Exemplarywelding processes are pulsed plasma arc, micro plasma arc, pulsed laser,and pulsed electron beam. The micro plasma arc is preferably applied atwelding currents between about 0.1 and 15 amps. In this manner, repairmaterial 50 can be welded to the spline 20 with a minimum of heat inputinto spline 20 to reduce the HAZ. If a wire feed is used, the wire ispreferably less than about 39.4 mils (˜1 mm) in diameter. It will beappreciated that welding repair material 50 onto spline 20 could beaccomplished with a manual or automated process, or a combination of thetwo. When using a pulsed electron beam weld, the welding process istypically accomplished with a voltage of about 100-140 kV and anamperage of about 5 to 10 mA. The pass rate is typically about 10-20inches per minute. It will be appreciated that any technique orcombination of techniques can be used, so long as the heat input iscontrolled to prevent excessive grain growth in the HAZ. Excessive graingrowth as used herein is an increase in grain size that adverselyaffects the material properties of the spline, preventing re-use of thespline.

Thus provided, repair material 50 is bonded to spline 20 while reducingthe HAZ adjacent the weld. In the embodiment provided, the HAZ grainsize can be within a desired range of less than ASTM Number 10, asdetermined by ASTM E112-96e2, Standard Test Methods for DeterminingAverage Grain Size. Grain sizes larger than a desired value aregenerally associated with promoting the propagation of fatigue cracks,which can lead to component failure.

Splines 20 are thin, narrow projections on shaft 10, and as such, it isdesirable to maintain the heat input as low as reasonably possible toreduce the effect of the HAZ on the pressure face 40 of each spline 20.If the heat input were not controlled, HAZ and grain growth may extendfrom the non-pressure face 42 through the spline 20 to the pressure face40, thereby negating the effectiveness of a repair. Thus, even thoughsome grain growth may occur, the low heat input limits the effects ofthe repair to the non-pressure face 42, which typically is not incontact with any other component during normal operation and thus theHAZ and grain growth if properly controlled and limited to thenon-pressure face 42 will not be a significant factor in fatigue.

As best seen in FIG. 4, repair material 50 is attached to the spline ina manner that results in a build-up of repair material 50 on thenon-pressure face 42. FIG. 4 further illustrates in phantom the contourof a repaired spline 20′ which includes a repaired pressure face 40′ anda repaired non-pressure face 42′. As will be appreciated, after theaddition of repair material 50, shaft 10 is remachined, or cut, creatinga repaired spline 20′.

In a preferred embodiment, the method of the present invention includesidentifying a repair area 45 on pressure face 40 of spline 20, weldingrepair material 50 to non-pressure faces 42, and machining shaft 10 toproduce repaired spline 20′. The repair area 45 is defined by the areaof spline 20 to be machined to provide a repaired pressure face 40′. Aswill be appreciated, to maintain symmetry and balance during operation,all splines 20 of shaft 10 will typically require a build up of repairmaterial 50 onto the non-pressure faces 42 to provide repaired splines20′. The pressure face 40 of each spline 20 is machined to the contourof repaired pressure face 40′. The non-pressure face 42 is preferablyalso machined to remove excess repair material 50 to produce repairednon-pressure face 42′. Thus provided, repaired splines 20′ are slightlyreclocked on shaft 10 when compared to the original radial locations ofsplines 20, but otherwise the repaired splines 20′ have dimensions thatare the same or nearly the same as the original splines 20 and withinfit-up tolerances. FIG. 5 illustrates a repaired spline 20′ aftercompletion of machining operations.

Thus provided, remachined pressure face 40′ of spline 20′ is comprisedof original forged shaft material and not of repair material 50. In thismanner, shaft 10 is provided with a wear surface that comprises theoriginal shaft materials. This original material retains the desiredphysical properties for splines 20 and, in using the method describedherein, has not been significantly altered by the welding process. Incontrast, a repair consisting of applying a repair material to wornportion and remachining a shaft to original dimensions would provide ashaft with contacting surfaces that may have undesirable properties. Itwill be appreciated that the process described herein, while preferablydirected to repairing splines 20 that have been worn due to normal use,could also be used, for example, to repair splines 20 that do notconform to required tolerances for whatever reason.

Repair material 50 is typically built up on non-pressure face 42 to athickness of less than about 40 mils, preferably less than about 15mils. The repair material may be applied in a plurality of passes, inorder to minimize heat input on any one pass. It will be appreciatedthat the build-up of repair material 50 is at least as thick as the wornportion 32 in order to restore the repaired spline 20′ to the samedimensions as the spline 20 prior to use and its subsequent wear. Thus,prior to the build-up of repair material, the thickness of the wornportion 32, and thus the thickness of the repair area of the pressureface 40, is typically determined normal to the worn surface 36.

Also preferred, repair material 50 is of identical material as shaft 10,which materials are typically superalloys selected from the groupconsisting of nickel-based, iron-based, cobalt-based, and combinationsthereof. Even more preferably, shaft 10 and repair material 50 areINCONEL® 718, although other suitable materials could be repaired usingthe method described herein. INCONEL® is a federally registeredtrademark owned by Huntington Alloys Corporation of Huntington, W. Va.The composition of INCONEL® 718 is well known in the art and is adesignation for a nickel-based superalloy comprising about 18 weightpercent chromium, about 19 weight percent iron, about 5 weight percentniobium+tantalum, about 3 weight percent molybdenum, about 0.9 weightpercent titanium, about 0.5 weight percent aluminum, about 0.05 weightpercent carbon, about 0.009 weight percent boron, a maximum of about 1weight percent cobalt, a maximum of about 0.35 weight percent manganese,a maximum of about 0.35 weight percent silicon, a maximum of about 0.1weight percent copper, and the balance nickel.

By welding the repair material 50 to the non-pressure face 42 of aspline 20, the HAZ of the repaired spline will be adjacent the repairednon-pressure face 42′ of repaired spline 20′. The grain size within thisHAZ may be larger than the grain size of original shaft 10 materialadjacent pressure face 40′. For applications involving a spline thatencounters a single rotational direction, and therefore a pressure faceand a non-pressure face on each spline, alteration of the physicalproperties, such as hardness and grain size, adjacent the pressure facemay impact the strength and service life of the component, whilealteration of physical properties adjacent the non-pressure face mayhave negligible impact on the strength and service life of thecomponent. Further heat treatment to alter the physical properties of ashaft, if desired, may be performed and is envisioned as a part of thesubject invention. Heat treatment is typically carried out at atemperature between about 1150° F. to about 1400° F. for up to about 16hours using standard ramp rates for the material selected to reach thetreatment temperature.

The use of wire feed welding methods may be used to repair splines inaccordance with exemplary embodiments of the invention. Whilesatisfactory results are achieved with wire feed welding, to achieve alevel of consistency and repeatability in a production environment, yetanother exemplary embodiment of the invention is provided.

According to another embodiment of the invention, a method for repairingthe splines involves the use of a sheath or overlay that fits over thesplines of the gas turbine shaft. The overlay covers and contacts thesplines and acts as a sacrificial source of repair material for welding.The use of an overlay provides better control over the amount of repairmaterial applied to the splines and thus provides better heat controlduring welding.

Referring to FIG. 6, an overlay 600 is a tubular device comprised of anyweld repair material, and preferably is INCONEL® 718. The overlay 600has an outer surface 620 and an inner surface 625 that defines anaperture 630 through which the splines 20 fit. The inner surface 625 isdimensioned to substantially match the geometry and dimensions of thesplines 20 so that when the overlay 600 is placed over the splines 20 ofthe shaft 10, the overlay 600 is substantially immobilized by a slip fitwith the splines 20 which are received by matching recesses formed alongthe inner surface 625 of the overlay 600.

The outer surface 620 of the overlay 600 may be defined by anycross-sectional area. For example, the outer surface 620 may be definedby a circular cross sectional area as shown in FIG. 6, while accordingto another exemplary embodiment of the invention, a cookie-cutter styleoverlay 700 as shown in FIG. 7 is used. As illustrated in FIG. 7, theoverlay 700 has a substantially uniform thickness, decreasing the amountof material needed to construct the overlay 700, in which both an outersurface 720 and an inner surface 725 of the overlay 700 substantiallymatch the contour of the splines 20.

Referring again to FIG. 6, the overlay 600 may have a series of parallelscribes lines 640 running along the length of the overlay 600. Thescribe lines 640 can be made using any method known in the art and arespaced on the outer surface 620 of the overlay 600 such that the scribelines 640 define alternating areas over the pressure face 40 andnon-pressure face 42 of the splines 20. Using a precision weldingdevice, a series of weld passes are made in the area between two scribelines 640, which area is over a non-pressure face of a spline 20.Preferably, the welds are made in a direction parallel to the scribelines. The weld causes a portion of the overlay 600 to bemetallurgically bonded as repair material to the non-pressure face 42 ofthe splines 20.

Once the area between the scribe lines 640 has been completely welded,the process is repeated with respect to the next set of scribe lines 640that define an area over a non-pressure face 42 of a spline 20, skippingevery other area defined by the scribe lines 640, which define an areaover a pressure face 40 of a spline 20 for which it is not desired toattach any repair material. When the overlay 600 has an outer surfacedefined by a circular cross-sectional area as shown in FIG. 6, thedistance from the outer surface 620 to the non-pressure face 42 of thespline 20, and the depth of the weld, changes with each pass. Usingprecision welding tools as are known to those of skill in the art,adjustments can be easily made after each pass to control the depth ofthe weld for the subsequent pass. The overlay 600 is of a sufficientthickness to allow heat from the weld to heat the inner surface 625 ofthe overlay 600 and thus result in the deposition of repair material onthe non-pressure face 42 of the splines.

The overlay 600 can be of any length, but is preferably at least as longas the splines 20 of the shaft 10 to avoid the need to use more than oneoverlay 600, and to permit a single, uninterrupted path along the lengthof each spline 20. Preferably, as shown in FIG. 7, the overlay 700 islonger than the splines 20. It will be appreciated that the lengths ofthe overlay shown in FIGS. 6 and 7 are for purposes of illustration andare not dependent on the shape of the overlay.

As will be appreciated, heat surge and the like are known to sometimesoccur at points of weld initiation or termination. Thus, if a weld isstarted or stopped directly over the spline 20 being repaired,variations of quality may occur in the weld resulting in localized areashaving undesirable properties. However, if the weld is initiated orstopped beyond the splines 20, a consistent weld can be achieved overthe entire length of the splines 20 and any heat surge occurs at an areaof the overlay 700 not in contact with the splines 20.

However, because the overlay 700 extends beyond the splines 20, thesplines 20 cannot be seen during the welding process. Accordingly, startand stop tabs 760, 770 may be provided that serve as markers on theouter surface 720 of points before and after the splines 20. The tabs760, 770 indicate that welding can be initiated or stopped with littlerisk of heat surge or other damage to the splines 20. It will beappreciated that the start and stop tabs 760, 770 may be used incombination with scribe lines to define an area for welding, althoughscribe lines may be unnecessary when using an overlay 700 having asubstantially constant thickness as illustrated in FIG. 7, in which thepeaks and valleys of the contoured outer surface 720 perform the samefunction as scribe lines.

Precision welding tools as are known in the art may be used toaccomplish the various welding processes of the invention using anoverlay. In this manner, the width and depth of a weld run can becontrolled so that the weld does not result in repair material from theoverlay being applied to the pressure face of any spline. Furthermore, aconsistent amount of repair material is applied to the splines. Afterwelding is complete, those portions of the overlay not attached by theweld, i.e., those portions contacting the pressure face of the splines,are easily removed during machining operations. As previously discussed,machining involves machining the pressure face of the spline to providea smooth surface comprised of as-manufactured shaft material. Thenon-pressure face is also machined to remove excess repair materialwhere the overlay was welded to provide the desired contour anddimensions of the spline.

It will be appreciated that while exemplary embodiments of the inventionhave been described with respect to splines of a gas turbine engineshaft, the principles of the invention apply equally to seal teeth andany other component of a gas turbine engine having splines, teeth,sprockets, or similar features.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. An apparatus for use in repairing one or more equally and radiallyspaced splines of an aircraft turbine engine shaft, the apparatuscomprising: a tubular overlay comprising a nickel-based superalloy, thetubular overlay having an outer surface and a substantially cylindricalinner surface, the substantially cylindrical inner surface having aplurality of equally and radially-spaced spline-receiving groovesconforming to a plurality of equally and radially spaced splines of anaircraft turbine engine shaft, each of the equally and radially-spacedspline-receiving grooves being substantially parallel to the major axisof the substantially cylindrical inner surface, the tubular overlayfurther having a plurality of tabs extending from the outer surface. 2.The apparatus of claim 1, wherein the tubular overlay has asubstantially constant thickness.
 3. The apparatus of claim 1, whereinthe cross-sectional area of the outer surface of the tubular overlay iscircular.
 4. The apparatus of claim 1, further comprising scribe lineson the outer surface of the tubular overlay.
 5. The apparatus of claim4, wherein the scribe lines are substantially parallel to the major axisof the substantially cylindrical inner surface.
 6. The apparatus ofclaim 1, wherein the tubular overlay comprises a nickel-based superalloycomprising about 18 weight percent chromium, about 19 weight percentiron, about 5 weight percent niobium+tantalum, about 3 weight percentmolybdenum, about 0.9 weight percent titanium, about 0.5 weight percentaluminum, about 0.05 weight percent carbon, about 0.009 weight percentboron, a maximum of about 1 weight percent cobalt, a maximum of about0.35 weight percent manganese, a maximum of about 0.35 weight percentsilicon, a maximum of about 0.1 weight percent copper, and the balancenickel.
 7. An apparatus for use in repairing one or more equally andradially spaced splines of an aircraft turbine engine shaft, theapparatus comprising: a tubular overlay comprising a nickel-basedsuperalloy, the tubular overlay having an outer surface and asubstantially cylindrical inner surface, the substantially cylindricalinner surface having a plurality of equally and radially-spacedspline-receiving grooves conforming to a plurality of equally andradially spaced splines of an aircraft turbine engine shaft, each of theequally and radially-spaced spline-receiving grooves being substantiallyparallel to the major axis of the substantially cylindrical innersurface, the outer surface having scribe lines.
 8. The apparatus ofclaim 7, wherein the scribe lines are substantially parallel to themajor axis of the substantially cylindrical inner surface.